This invention relates to a processing solution for the silver complex diffusion transfer process and a processing method by using said solution.
The principle of the silver complex diffusion transfer process (hereinafter referred to as DTR process) is well known from the description in U.S. Pat. No. 2,352,014 and many other patents and literature. In DTR process, the silver complex is imagewise transferred by diffusion from a silver halide emulsion layer to an image receptive layer and transformed therein into a silver image generally in the presence of physical development nuclei. For this purpose, the imagewise exposed silver halide emulsion layer is arranged so as to be in contact with or is brought into contact with the image receptive layer in the presence of a developing agent and a solvent for the silver halide, thereby to convert the unexposed silver halide into a soluble silver complex. In the exposed areas of the silver halide emulsion layer, the silver halide is developed into silver which is insoluble and, hence, cannot diffuse. In the unexposed areas of the silver halide emulsion layer, the silver halide is converted into a soluble silver complex and is transferred to an image receptive layer wherein the silver complex formes a silver image generally in the presence of development nuclei.
The DTR process can be utilized in a wide field such as reproduction of documents, making of printing plates, preparation of block copies, and instant photography.
Particularly in reproducing documents or preparing block copies, a negative material having a silver halide emulsion layer is brought into close contact with a positive material having an image receptive layer in a DTR processing solution generally containing a silver-complexing agent, thereby to form a silver image receptive layer of the positive material. The silver mage in these cases is required to be pure black or bluish black in color and sufficiently high in density. It is also important that the silver image be high in contrast and sharpness, excellent in image reproducibility, and preferably high in transfer speed. In addition, these properties of the positive material should not be greatly dependent upon the processing conditions such as, for example, processing time and temperature.
It is easily presumable from the principle of DTR process that the process of image formation is greatly affected by the processing conditions, especially temperature and speed of processing, and this fact is well known to the art.
As examples of general characteristics of the formed image affected by the environmental processing conditions, particularly processing temperature and conditions of conveyance in DTR process, there may be mentioned the following:
1. Change in sensitivity, general tone, color tone, and density (both reflection and transmission densities).
2. Increased tendency of staining (due to formation of fine grains of silver colloid) on the image receptive sheet.
3. Decreased ability of forming minute images such as fine lines or fine dots with the increase in processing temperature or the decrease in rate of conveyance.
Although a large number of processing solutions have been proposed to solve the above problems, as disclosed in, for example, Japanese Patent Application "Kokai" (Laid-open) Nos. 93, 338/73, 79, 445/80, 157, 738/80, 176, 036/82, and 72, 143/83, yet none of these provides a means to solve collectively the above problems. In the background of the circumstances, there seems to be a general belief such that the DTR process is difficult to control, because the process is based on a delicate balance among chemical development, dissolution, diffusion, and physical development.
Moreover, on continual and long-term use of the processing solution (hereinafter referred to as running processing), the above change of characteristics become pronounced and other changes will take place.
The image formation system for the DTR process generally employs a simplified line of apparatuses. For instance, a processor is composed of a tray to hold a transfer developer, a pair of squeeze rollers to bring a negative sheet and a positive sheet into close contact, and a motor to drive the rollers. In such a system, even when no material is processed, a conventional running solution will retain its processing characteristics only for several days; and when photographic materials are continually processed, the running solution will become exhausted in a shorter period of time.